The present invention relates generally to optical emitters and detectors, and optical position tracking devices, in particular, optical devices having distinct radiation and detection properties that may be used to track position of objects, using a relatively small number of optical elements.
Position tracking is a growing technology with ever increasing applications. For example, in the entertainment arena, position tracking in three dimensions is used in virtual reality simulation. Position tracking is also used in the industrial arena, with applications in process control and robotics. The field of biomedics also uses position tracking devices for tracking portions of a human body to determine the body's motion patterns. Similarly in animation dynamics, the tracking of multiple body parts is used for controlling animated figures. Many other applications exist, for which position tracking is useful if not advantageous.
Conventional position tracking can be broken down into two broad technologies, i.e., active systems and passive systems. Active systems utilize active electronic elements on the objects being tracked. For example, the Polhemus' 3SPACE ISOTRACK II.RTM. system uses active magnetic elements to create a dynamic magnetic field that is representative of the body's position. By sensing changes in the magnetic field, the system delivers all six axes of the object's spatial location.
Active systems are generally high-performance, high-end products. However, they can have disadvantages, including limited range of motion, metal interference, complex operation and high cost. In particular, the range of the magnetic field is typically limited, and trailing connection wires are often a nuisance. Where the area of motion contains substantial metal, mapping of the entire field is usually part of the system's required initialization.
In contrast, passive systems track objects without physical links between the object and the system. Target points such as retro reflectors may be used, or image processing of a video image may be performed. While passive systems are often less complex and less expensive compared to active systems, they are often lacking in resolution. Thus, for object recognition, passive systems typically require extensive image processing, which can increase costs and the probability of errors. The use of reflectors avoids some of these problems, but not without introducing other problems, such as the need for critical alignment and extensive initialization.
Aside from the various system limitations discussed above, the sensing components of an optical detector, such as photodiodes or charge-coupled device (CCD), have their own limitations. While these components can be made directionally-sensitive (e.g., with the provision of a slit, or the use of Gray-coded multi-element arrays), the response is often limited. For example, they typically provide directional information or resolution about one axis only, and the sensor's accuracy is typically limited by the number of optical elements provided.
It should therefore be appreciated that there exists a definite need for a relatively simple and inexpensive position tracking system, which can track the position of an object along at least three axes, if not all six axes to include objection rotation, using minimal electrical and/or optical elements. It is desired that the system has low alignment and initialization requirements and low processing demands. In that regard, it is desired that the system be structurally and electronically simple, while remaining capable of providing at least directional indicative of the direction along which the object is positioned relative to the system. It is further desired that the system be able to provide locational data inclusive of range data, along with directional data, for tracking an object in three dimensional space. The present invention addresses all of these desires and more.